MediaWiki Developer's Handbook/Add JavaScript/Adding a purge tab

function purge(){//Here, we declare the function and it's parametersvar hist;var url;//Here, we declare two variablesif(!(hist = document.getElementById('ca-history')))return;//Try to set hist as the document's element//with id 'ca-history' - tha's the history tabif(!(url = hist.getElementsByTagName('a')[0]))return;//Try to set url as the history tab's first//element with the tag 'a'if(!(url = url.href))return;//Try to set url as the href of that element from line 3
addPortletLink('p-cactions',//add a PortletLink to the p-cactions area (the tabs at the top of the page)
url.replace(/([?&]action=)history([&#]|$)/,'$1purge$2'),//replace the ?action=history//part of the href we got from//the history tab with ?action=purge,//and set it as the destination'purge',//set the text that will appear on the tab'ca-purge',//set the internal id for the tab - this is useful for//referring to it, and positioning tabs relative to one another'Purge server cache for this page',//set the mouseover text'0');//the access key}if( wgCanonicalNamespace !="Special") addOnloadHook(purge);//if it's not a special page then hook onto the page loading//and run the function purge